src/utf8_utils.cpp

/*
 *  Copyright (C) 1999 Tom Tromey
 *  Copyright (C) 2000 Red Hat, Inc.
 *  Copyright (C) 2004-2021 Savoir-faire Linux Inc.
 *
 *  Author: Pascal Potvin <pascal.potvin@extenway.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA.
 */

#include <cstring>
#include <cassert>
#include "utf8_utils.h"

#if defined(_MSC_VER)
#include <BaseTsd.h>
using ssize_t = SSIZE_T;
#endif

/*
 * The LIKELY and UNLIKELY macros let the programmer give hints to
 * the compiler about the expected result of an expression. Some compilers
 * can use this information for optimizations.
 */
#if defined(__GNUC__) && (__GNUC__ > 2) && defined(__OPTIMIZE__)
#define LIKELY(expr)   (__builtin_expect(expr, 1))
#define UNLIKELY(expr) (__builtin_expect(expr, 0))
#else
#define LIKELY(expr)   (expr)
#define UNLIKELY(expr) (expr)
#endif

/*
 * Check whether a Unicode (5.2) char is in a valid range.
 *
 * The first check comes from the Unicode guarantee to never encode
 * a point above 0x0010ffff, since UTF-16 couldn't represent it.
 *
 * The second check covers surrogate pairs (category Cs).
 *
 * @param Char the character
 */
#define UNICODE_VALID(Char) ((Char) < 0x110000 && (((Char) &0xFFFFF800) != 0xD800))

#define CONTINUATION_CHAR \
    if ((*(unsigned char*) p & 0xc0) != 0x80) /* 10xxxxxx */ \
        goto error; \
    val <<= 6; \
    val |= (*(unsigned char*) p) & 0x3f;

namespace jami {

bool utf8_validate_c_str(const char* str, ssize_t max_len, const char** end);

static const char*
fast_validate(const char* str)
{
    char32_t val = 0;
    char32_t min = 0;
    const char* p;

    for (p = str; *p; p++) {
        if (*(unsigned char*) p < 128)
            /* done */;
        else {
            const char* last;

            last = p;

            if ((*(unsigned char*) p & 0xe0) == 0xc0) { /* 110xxxxx */
                if (UNLIKELY((*(unsigned char*) p & 0x1e) == 0))
                    goto error;

                p++;

                if (UNLIKELY((*(unsigned char*) p & 0xc0) != 0x80)) /* 10xxxxxx */
                    goto error;
            } else {
                if ((*(unsigned char*) p & 0xf0) == 0xe0) { /* 1110xxxx */
                    min = (1 << 11);
                    val = *(unsigned char*) p & 0x0f;
                    goto TWO_REMAINING;
                } else if ((*(unsigned char*) p & 0xf8) == 0xf0) { /* 11110xxx */
                    min = (1 << 16);
                    val = *(unsigned char*) p & 0x07;
                } else
                    goto error;

                p++;
                CONTINUATION_CHAR;
            TWO_REMAINING:
                p++;
                CONTINUATION_CHAR;
                p++;
                CONTINUATION_CHAR;

                if (UNLIKELY(val < min))
                    goto error;

                if (UNLIKELY(!UNICODE_VALID(val)))
                    goto error;
            }

            continue;

        error:
            return last;
        }
    }

    return p;
}

static const char*
fast_validate_len(const char* str, ssize_t max_len)
{
    char32_t val = 0;
    char32_t min = 0;
    const char* p;

    assert(max_len >= 0);

    for (p = str; ((p - str) < max_len) && *p; p++) {
        if (*(unsigned char*) p < 128)
            /* done */;
        else {
            const char* last;

            last = p;

            if ((*(unsigned char*) p & 0xe0) == 0xc0) { /* 110xxxxx */
                if (UNLIKELY(max_len - (p - str) < 2))
                    goto error;

                if (UNLIKELY((*(unsigned char*) p & 0x1e) == 0))
                    goto error;

                p++;

                if (UNLIKELY((*(unsigned char*) p & 0xc0) != 0x80)) /* 10xxxxxx */
                    goto error;
            } else {
                if ((*(unsigned char*) p & 0xf0) == 0xe0) { /* 1110xxxx */
                    if (UNLIKELY(max_len - (p - str) < 3))
                        goto error;

                    min = (1 << 11);
                    val = *(unsigned char*) p & 0x0f;
                    goto TWO_REMAINING;
                } else if ((*(unsigned char*) p & 0xf8) == 0xf0) { /* 11110xxx */
                    if (UNLIKELY(max_len - (p - str) < 4))
                        goto error;

                    min = (1 << 16);
                    val = *(unsigned char*) p & 0x07;
                } else
                    goto error;

                p++;
                CONTINUATION_CHAR;
            TWO_REMAINING:
                p++;
                CONTINUATION_CHAR;
                p++;
                CONTINUATION_CHAR;

                if (UNLIKELY(val < min))
                    goto error;

                if (UNLIKELY(!UNICODE_VALID(val)))
                    goto error;
            }

            continue;

        error:
            return last;
        }
    }

    return p;
}

/**
 * utf8_validate_c_str:
 * @str: a pointer to character data
 * @max_len: max bytes to validate, or -1 to go until NULL
 * @end: return location for end of valid data
 *
 * Validates UTF-8 encoded text. @str is the text to validate;
 * if @str is nul-terminated, then @max_len can be -1, otherwise
 * @max_len should be the number of bytes to validate.
 * If @end is non-%NULL, then the end of the valid range
 * will be stored there (i.e. the start of the first invalid
 * character if some bytes were invalid, or the end of the text
 * being validated otherwise).
 *
 * Note that utf8_validate() returns %false if @max_len is
 * positive and any of the @max_len bytes are nul.
 *
 * Returns true if all of @str was valid. Dbus requires valid UTF-8 as input;
 * sip packets should also be encoded in utf8; so data read from a file or the
 * network should be checked with utf8_validate() before doing anything else
 * with it.
 *
 * Returns: true if the text was valid UTF-8
 */
bool
utf8_validate_c_str(const char* str, ssize_t max_len, const char** end)
{
    const char* p;

    if (max_len < 0)
        p = fast_validate(str);
    else
        p = fast_validate_len(str, max_len);

    if (end)
        *end = p;

    if ((max_len >= 0 && p != str + max_len) || (max_len < 0 && *p != '\0'))
        return false;
    else
        return true;
}

bool
utf8_validate(const std::string& str)
{
    const char* p;

    p = fast_validate(str.c_str());

    return (*p == '\0');
}

std::string
utf8_make_valid(const std::string& name)
{
    ssize_t remaining_bytes = name.size();
    ssize_t valid_bytes;
    const char* remainder = name.c_str();
    const char* invalid;
    char* str = NULL;
    char* pos;

    while (remaining_bytes != 0) {
        if (utf8_validate_c_str(remainder, remaining_bytes, &invalid))
            break;

        valid_bytes = invalid - remainder;

        if (str == NULL)
            // If every byte is replaced by U+FFFD, max(strlen(string)) == 3 * name.size()
            str = new char[3 * remaining_bytes];

        pos = str;

        strncpy(pos, remainder, valid_bytes);
        pos += valid_bytes;

        /* append U+FFFD REPLACEMENT CHARACTER */
        pos[0] = '\357';
        pos[1] = '\277';
        pos[2] = '\275';

        pos += 3;

        remaining_bytes -= valid_bytes + 1;
        remainder = invalid + 1;
    }

    if (str == NULL)
        return std::string(name);

    strncpy(pos, remainder, remaining_bytes);
    pos += remaining_bytes;

    std::string answer(str, pos - str);
    assert(utf8_validate_c_str(answer.c_str(), -1, NULL));

    delete[] str;

    return answer;
}

} // namespace jami